Problem with elevation (not accurate at all)

[levydanqc]

Hi,
I know it's been some time since this project was publish, but I'm trying to read elevations for these coordinates : 46.75303,-71.40358 and it doesn't work at all.
Any coordinates for Quebec, Qc, CA, return values not even close.

Hoping to find a solution.

[nicholas-fong]

The snippet below (tile N46W072.hgt) should work in all four quadrants.
Your POI is (46.75303, -71.40358) = 55 m
Parc naturel du mont Bélair (46.822845, -71.507354) = 483 m
Mont Roland-J.-Auger (46.845798, -71.472764) = 330 m.
on OpenStreetMap:
Parc naturel du mont Bélair = 484 m
Mont Roland-J.-Auger = 335 m.

import math
import numpy as np

def read_elevation(hgt_file, lon, lat):
    with open(hgt_file, 'rb') as hgt_data:
        # Each data point is a 16bit signed integer(i2) big endian(>)
        height = np.fromfile(hgt_data, np.dtype('>i2'), 1201*1201).reshape((1201, 1201))
        if ( lat >= 0.0 ):                    #first and second quadrants
            x = round (1200 - lat%1 * 1200) 
            y = round ( lon%1 * 1200 )
            return height[ x, y ].astype(np.int16)
        if ( lat < 0.0 ):                     #third and fourth quadrants
            x = round ((1 - lat%1) * 1200)
            y = round ( lon%1 * 1200 )
            return height[ x, y ].astype(np.int16)

def find_tile ( longitude, latitude ):
    if  ( latitude >= 0.0 and longitude >= 0.0 ):
        hemi, meri = "N", "E"
        t1 = f"{math.floor(latitude):02d}"
        t2 = f"{math.floor(longitude):03d}"
    elif ( latitude >= 0.0 and longitude < 0.0 ):
        hemi, meri = "N", "W"
        t1 = f"{math.floor(latitude):02d}"
        t2 = f"{math.ceil(abs(longitude)):03d}"
    elif ( latitude < 0.0 and longitude < 0.0 ):
        hemi, meri = "S", "W"
        t1 = f"{math.ceil(abs(latitude)):02d}"
        t2 = f"{math.ceil(abs(longitude)):03d}"
    elif ( latitude < 0.0 and longitude >= 0.0 ):
        hemi, meri = "S", "E"
        t1 = f"{math.ceil(abs(latitude)):02d}"
        t2 = f"{math.floor(longitude):03d}"
    return( f"{hemi}{t1}{meri}{t2}.hgt" ) 

[nicholas-fong]

See this module which is versatile in reading tiles from different sources.

https://github.com/nicholas-fong/SRTM-GeoTIFF